(1) Field of the Invention
The present invention relates to an oxygen absorbing multi-layer film with excellence in strength, heat resistance, sealing properties and appearance, and a packaging container using this oxygen absorbing multi-layer film.
(2) Description of the Related Art
In recent years, as one packaging technique, there have been developed packaging containers which are made of a multi-layer material having an oxygen absorbing layer comprising an oxygen absorbing resin composition obtained by blending a thermoplastic resin with a deoxidizing agent and which intend to improve the gas barrier properties of the containers themselves and to impart an oxygen absorbing function thereto. The packaging containers having the oxygen absorbing function are each made of an oxygen absorbing multi-layer material constituted of an oxygen absorbing resin layer as an intermediate layer including the deoxidizing agent, a gas barrier outer layer of a package outside and an oxygen permeating inner layer of a package inside. These packaging containers are molded into bags, cups, trays, bottles and the like, and hence they have now been developed as such containers.
As the oxygen absorbing multi-layer materials, for example, in Japanese Patent Application Laid-open Nos. 72851/1990 and 90848/1992, there have been described oxygen absorbing multi-layer materials each having an oxygen absorbing layer as an intermediate layer obtained by dispersing an iron-including deoxidizing agent in a resin. Moreover, in Japanese Patent Application Laid-open No. 72941/1996, a technique has been suggested which intends to improve the oxygen absorption performance of the oxygen absorbing multi-layer material. Furthermore, in Japanese Patent Application Laid-open Nos. 132573/1996 and 40024/1997, improved techniques of the oxygen absorbing multi-layer materials have been described in which a polyolefin layer is interposed between a deoxidizing agent-including resin layer and a gas barrier layer.
As the deoxidizing agent which is blended in the oxygen absorbing layer of the oxygen absorbing multi-layer material, an iron-including deoxidizing agent is usually used. In the case that the oxygen absorbing layer comprising an oxygen absorbing resin composition blended with the iron-including deoxidizing agent is used as an oxygen absorbing multi-layer container for the preservation of a food or the like, the color of an iron powder blended in the oxygen absorbing layer and the color of an iron rust due to the absorption of oxygen in the container are visually observed at the time of the opening of the container, so that the appearance of a material such as the food to be preserved is impaired on occasion. As measures against this inconvenience, there is a technique in which a white pigment or a colored pigment is added to an oxygen permeating layer or to an oxygen absorbing layer, thereby concealing the iron powder contained in the oxygen absorbing layer.
In the technique of adding the pigment to the resin, however, the resin content in the oxygen absorbing layer containing the iron powder and the oxygen permeating layer containing the pigment is low, so that adhesive properties are weak, with the result that the impact resistance, tear strength and stick strength required for a packaging material inconveniently deteriorate. Additionally, in the case that such a packaging material is molded into packaging containers such as bags, heat-sealing properties and hot tack properties disadvantageously deteriorate.
An object of the present invention is to provide an oxygen absorbing multi-layer film having an oxygen absorbing layer comprising an oxygen absorbing resin composition containing a deoxidizing agent, which film is excellent in tear strength, stick strength, impact resistance, heat resistance, heat-sealing properties, hot tack properties and appearance.
Another object of the present invention is to provide an oxygen absorbing packaging container in which the above-mentioned oxygen absorbing multi-layer film is used.
The present inventors have intensively researched and investigated in order to solve the above-mentioned problems of oxygen absorbing multi-layer materials having deoxidizing agent-containing resin layers, and as a result, the above-mentioned problem which the conventional oxygen absorbing multi-layer materials have can be solved by arranging an oxygen permeating layer 1 comprising two layers of an uncolored layer 11 and a color concealing layer 12 inside an oxygen absorbing layer 2 comprising an oxygen absorbing resin composition obtained by blending an oxygen permeating thermoplastic resin with a deoxidizing agent, and then placing the uncolored layer 11 so as to be a surface layer. On the basis of this finding, the present invention has been completed.
The present invention is directed to an oxygen absorbing multi-layer film which comprises an oxygen permeating layer 1 comprising an oxygen permeating polyolefin which is one surface, a gas barrier layer 3 which is another surface, and an oxygen absorbing layer 2 sandwiched between these layers, and comprising an oxygen absorbing resin composition obtained by adding an iron-containing deoxidizing agent to an oxygen permeating polyolefin, the oxygen permeating layer 1 being constituted of two layers of an uncolored layer 11 and a color concealing layer 12, the colored layer 11 being a surface layer.
In addition, the present invention is also directed to an oxygen absorbing packaging container at least partially made of the above-mentioned oxygen absorbing multi-layer film in which the oxygen permeating layer 1 is used as an inner layer of the container.
The oxygen absorbing multi-layer film and the oxygen absorbing packaging container comprising this film according to the present invention are characterized in that the oxygen permeating layer 1 which is in contact with the oxygen absorbing layer 2 is constituted of two layers of the uncolored layer 11 and the color concealing layer 12, and the colored layer 11 is the surface layer, and so they are excellent in heat resistance, impact resistance, stick strength, tear strength, heat-sealing properties, hot tack properties and appearance. These features facilitate liquid filling, powder filling and automatic high-speed solid filling, and also enable a material packed in a packaging container to be preserved as such after a heat treatment such as a boiling treatment or a retort treatment, whereby further long-term preservation is made possible.